Tonight and the coming week you can use the moon as a celestial mouse as you browse across the late spring sky.
With your telescope you can have all kinds of fun checking out the moon with its craters and dark lunar plains. And, if atmospheric conditions are just right, you may see the rest of the moon’s disk beside the directly sunlit crescent part.
That’s a phenomenon called Earthshine, because that’s just what it is. It’s second-hand sunlight that bounces off the Earth and bathes the dark part of the moon’s disk in a pale grayish light. It can be a lovely sight.
Tonight will be the big show, when the moon will be smooching up to both Saturn and the bright star Regulus. Even if you’re not all that much into stargazing, I know you’ll like what you see.
Regulus, the brightest star in the constellation Leo, is closest to the moon. Saturn is a little farther away, but is definitely brighter than Regulus.
The moon slips to the east among the background of stars from night to night as it orbits our Earth. Saturn also migrates against the backdrop of stars, much more slowly, as it circles the sun every 29 years. It happens that tonight the moon, Saturn and Regulus find themselves in close celestial company, at least visually.
The moon will be a little more than 240,000 miles from Earth, Saturn is 883 million miles away, and Regulus is 78 light-years, or about 458 trillion miles away. The light we see tonight from Regulus left that star in 1930. How many of you were even around in 1930?
This is really the last call to point your telescope at Saturn this year. It’s leaving our evening skies as Earth, in its orbit around the sun, is turning away from the direction of the constellation Leo and the planet Saturn. By the end of the month it will be too low in the western sky at start of darkness to really see it clearly.
Also, by the time it comes back to the evening sky next year, its ring system will be on edge to our view on Earth and will be more or less invisible. We really won’t get a good look at Saturn’s ring system again until the spring of 2010. Take a good last look at the ring system that stretches across a diameter of more than 130,000 miles, but is only about 15 to 30 miles thick.
If your scope is large enough you may also see some of Saturn’s moons, which look like tiny stars swarming the planet. The easiest one to see is Titan, Saturn’s largest moon at more than 3,200 miles in diameter, bigger than the planet Mercury.
By Thursday night the moon will have migrated far enough to the east to be sneaking a celestial kiss with the bright star Spica. By then, it will be a fatter moon as it approaches full next week.
Spica is the 11th brightest star in our sky, and is the brightest star in the large but dim constellation Virgo. It’s more than 260 light-years away, and is one of those stars that prove looks are deceiving, because it’s not just a single star, as it appears to the naked eye, but two stars orbiting each other every 4 days.
In astronomical terms it’s called an eclipsing binary star system, with the individual stars about 12 million miles apart. The brighter of the two is thought to be nearly eight times the diameter of our sun and cranks out more than 4,000 times the light of our home star.
Even to the naked eye, Spica appears to have a bluish tinge, indicating that it’s a hot star. Most astronomers believe the temperature at its outer layer is around 40,000 degrees, almost four times the temperature of our sun.
Next week the moon will pass by the star Antares, one of the biggest stars in this part of the Milky Way Galaxy. I’ll have more on that next week, along with the great story of the constellation Leo, the lion.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com
The Everett Astronomical Society welcomes new members and puts on public star parties. The Web site is members.tripod.com/everett_astronomy.
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